The present invention is directed to crosslinking compositions and mixtures for forming crosslinked high glass transition polymer systems.
High glass transition temperature polymers have been useful for a number of high temperature applications. Crosslinking generally improves high temperature performance, strength and chemical resistance compared to the base polymer. However, crosslinking of high glass temperature polymers to form polymers having the desired high temperature properties is generally not known in the art. For example, in previous attempts to crosslink high glass transition temperature (Tg) polymers the thermal stability of the polymer is compromised. This is particularly true for those high Tg polymers wherein the desired temperature for reaction (cure) may range from 200-450° C.
Crosslinking has been recognized as one way to address the requirements of high performance polymeric materials. Past attempts have used various different approaches for crosslinking polymers. One such attempt is described, for example, in U.S. Pat. No. 6,060,170, which is assigned to one of the assignees of the present application and is incorporated by reference in its entirety. The U.S. Pat. No. 6,060,170 describes the use of poly(arylene ether) polymer compositions having aromatic groups grafted on the poly(arylene ether) backbone, whereby the grafts allow for crosslinking of the polymers in a temperature range of from 200 to 450° C. One of the limitations of the U.S. Pat. No. 6,060,170 includes the requirement of the polymer to be dissolved in an appropriate solvent for grafting the crosslinking group. Such required process steps make grafting difficult or impossible for certain polymers, such as polyether ether ketone (PEEK).
U.S. Pat. No. 5,658,994, which is also assigned to one of the assignees of the present application and is incorporated by reference in its entirety, describes the use of poly(arylene ethers) as low dielectric interlayers for the electronics industry wherein the poly(arylene ether) may be crosslinked, for example, by crosslinking itself, through exposure to temperatures of greater than approximately 350° C., or alternatively by providing a crosslinking agent. In addition, the U.S. Pat. No. 5,658,994 also teaches end capping the polymer with known end cap agents, such as phenylethynyl, benzocyclobutene, ethynyl, and nitrile. The U.S. Pat. No. 5,658,994 shows a limit in the degree of crosslinking due to the crosslinking agent only being present at the end of the polymer chain. Crosslinking occurs only at the ends, therefore there are no crosslinks between mid-portions of the polymer chains. The limited degree of crosslinking results in a lower than desired glass transition temperature, reduced chemical resistance, as well as mechanical properties that are below desired levels.
International Patent Application Publication WO/2010/019488, which is incorporated by reference in its entirety, discloses the use of per(phenylethynyl)arenes as additives for crosslinking poly(arylene ether)s, polyimides, polyureas, polyurethanes, or polysulfones. The patent application does not disclose crosslinking, but utilizes a semiinterpenetrating polymer network between two polymers to provide improved properties.
The references Hedberg, F. L.; Arnold, F. E; J. Polym. Sci., Polym. Chem. Ed. 10 (1976) 14, 2607-19 and Banihashemi, A; Marvel, C. S.; J. Polym. Sci., Polym. Chem. Ed. (1977) 15, 2653-65, each of which is incorporated by reference in their entirety, disclose the preparation of polyphenylquinoxalines with pendant phenylethynyl groups and their thermal cure via intramolecular cycloaddition and the heating of the 2,2′-di(phenylethynyl)biphenyl moiety to produce a 9-phenyldibenz[a,c]anthracene moiety which enhances the Tg of the polymer. The Hedberg and Banihashemi are similar to the to the U.S. Pat. No. 5,658,994 discussed above, which is limited in the degree of crosslinking due to the crosslinking agent only being present at the end of the polymer chain. Crosslinking occurs only at the ends, therefore there are no crosslinks between mid-portions of the polymer chains. The limited degree of crosslinking results in a lower than desired glass transition temperature, reduced chemical resistance, as well as mechanical properties that are below desired levels.
The references Hergenrother, P. M.; Macromolecules (1981) 14, (4) 891-897; and Hergenrother, P. M.; Macromolecules (1981) 14, (4) 898-904, each of which is incorporated by reference in their entirety, disclose the preparation of poly(phenylquinoxalines) containing pendent phenylethynyl groups along the backbone, where these materials were prepared for evaluation as precursors for high thermally stable thermosets. The preparation of the poly(phenylquinoxalines) containing pendent phenylethynyl groups requires the synthesis of the poly(phenylquinoxalines) with monomers containing the phenylethynyl groups. The synthesis disclosed in the Hergenrother article is complicated and provides expensive processing and materials.
U.S. Pat. No. 5,138,028 and EP Patent Application No. 443352 A2 910828, each of which is incorporated by reference in their entirety, describes the preparation of polyimides, polyamic acids, polyamic acid esters, and polyisoimides which are end-capped with diarylacetylenes. The cured products can be used for encapsulation of electronic devices, as adhesives, and as moldings. The U.S. Pat. No. 5,138,028 and the EP Patent Application No. 443352 A2 910828 are similar to the to the U.S. Pat. No. 5,658,994 discussed above, which is limited in the degree of crosslinking due to the crosslinking agent only being present at the end of the polymer chain. Crosslinking occurs only at the ends, therefore there are no crosslinks between mid-portions of the polymer chains. The limited degree of crosslinking results in a lower than desired glass transition temperature, reduced chemical resistance, as well as mechanical properties that are below desired levels.
International Patent Application Publication WO 97/10193, which is incorporated by reference in its entirety, discloses various multi-phenylethynyl compounds which can be used for coating a wide variety of substrates such as computer chips. The reference Zhou, Q et al., Polym. Preprint (1993) 34(1), 193-4, which is incorporated by reference in its entirety, describes the preparation of carbon ladder polymers via the cyclization reactions of acetylenes. The WO 97/10193 publication discloses insitu formation of the polymer, wherein the carbon ladder polymers are insoluble. The synthesis disclosed in the WO 97/10193 publication is complicated and provides expensive processing and materials. In addition, the insolubility of the carbon ladder polymers provides substantial limits to the processing capabilities of the method.
U.S. Pat. No. 5,179,188, which is incorporated by reference in its entirety, describes polymers (oligomers) such as those described in U.S. Pat. No. 5,114,780, which are end-capped with reactive groups having double and triple bonds. Crosslinking occurs only at the ends, therefore there are no crosslinks between mid-portions of the polymer chains. The limited degree of crosslinking results in a lower than desired glass transition temperature, reduced chemical resistance, as well as mechanical properties that are below desired levels.
International Patent Application Publication WO/91/16370, which is incorporated by reference in its entirety, describes crosslinkable fluorinated aromatic ether compositions. The WO 91/16370 publication is similar to the to the U.S. Pat. No. 5,658,994 discussed above, which is limited in the degree of crosslinking due to the crosslinking agent only being present at the end of the polymer chain. Crosslinking occurs only at the ends, therefore there are no crosslinks between mid-portions of the polymer chains. The limited degree of crosslinking results in a lower than desired glass transition temperature, reduced chemical resistance, as well as mechanical properties that are below desired levels. In addition, the method of the WO 91/16370 publication is sensitive to molecular weight differences, which results in non-uniform crosslinking.
International Patent Application Publication WO/2010/019488, which is incorporated by reference in its entirety, discloses preparation of phenylethynylated monomers for use in preparing polymers which can be thermally crosslinked. The method disclosed in the WO/2010/019488 publication discloses a process that has a limited number of polymers that are suitable, as the polymer disclosed is made only with monomers containing the phenylethynyl groups.
There is a need in the art for polymeric materials with thermal stability at high temperatures, such as temperatures up to 500° C. A method and composition that crosslinks high glass transition polymers to form thermally stable, crosslinked polymer systems, would be desirable in the art.